Author Topic: Lunar Caves  (Read 33629 times)

Offline redliox

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Lunar Caves
« on: 08/22/2019 12:25 am »
Setting up a thread for discussing lunar caves, namely the lava tubes and skylights.  If any missions, such as the proposed Moon Diver, get underway for visiting them post here too.

The first 2 questions I wish to poise are:

1) How many skylights and lava tube locations are currently known on the Moon?

2) Are any sites known to exist within the South Pole–Aitken basin?
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Offline Tywin

Re: Lunar Caves
« Reply #1 on: 08/22/2019 12:59 am »
ESA is study the concept for explore this Lunar Caves too...

https://www.esa.int/Our_Activities/Preparing_for_the_Future/Discovery_and_Preparation/Seeking_innovative_ideas_for_exploring_lunar_caves

Adding this interesting video about the Moon Dive...


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Offline Dean47

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Re: Lunar Caves
« Reply #2 on: 08/23/2019 05:49 pm »
I predict that lunar caves will be surprisingly useful.  For instance, I don't think we should discount the value of lava tubes as cold traps for lunar water and other volatiles.  I have visited several lava tubes in the American west and am always amazed at how well they can trap and preserve ice well into the summer.  The same events that deposited water at the lunar poles should have deposited water in lunar caves that have natural access to the surface, assuming the underground tube goes far enough that parts of it are in permanent shadow.  Although the amount of water captured in a cave should be MUCH less than that at a polar location because of the much smaller capture area, it could be enough to support a small lunar base for a significant period. 

Offline Phil Stooke

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Re: Lunar Caves
« Reply #3 on: 08/23/2019 06:08 pm »
To answer the questions in the first post:

Distribution, formation mechanisms, and significance of lunar pits
Robert V. Wagner and Mark S. Robinson.
Icarus v. 237, pp. 52-60, 2014.
https://doi.org/10.1016/j.icarus.2014.04.002

-----------------
Highlights
We developed an algorithm to search for collapse pits in LROC NAC images.
We found ten pits in maria and highlands, typically 40–100 m in diameter and depth.
We found over 200 pits in impact melt, which average 16 m in diameter and 7 m in depth.
Pits are often significantly younger than their host materials.
Some pits have confirmed overhangs, and may connect to larger sublunarean voids.

I don't think any are in the SPA basin, though a prominent one is in Mare Ingenii on the northwest edge of SPA.  Pascal Lee has noted some possible pits in a crater at a high northern latitude where ice would be particularly likely.  Note I say 'possible' pits, they need further study.

There would be no advantage to having a pit in SPA, it's a scientifically interesting area but far from being the ideal place for a human habitat, if that was the goal.

Offline libra

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Re: Lunar Caves
« Reply #4 on: 08/23/2019 08:28 pm »
I'm fascinated by lunar caves and recently gathered links and documents about them, could dump some here in anybody interested.

There is the Marius Hill Hole (MHH) found by Kagyua in 2009 and imaged by LRO. A 200 ft wide opening.

I've seen papers explaining that thanks to the very low lunar gravity those caves could be as wide as 3 miles. It completely blew my mind.

Imagine the numbers of Bigelow inflatables that could be chained like sausages into such a cave. Plenty enough for a space colony, easier than in deep space or lunar surface, much closer than Mars... of course the interior of the cave would need serious "cleaning" in the first place.

Offline Tywin

Re: Lunar Caves
« Reply #5 on: 08/23/2019 08:35 pm »
Yes please, share that papers... :)
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Online FutureSpaceTourist

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Re: Lunar Caves
« Reply #6 on: 07/26/2022 09:46 pm »
https://twitter.com/nasamoon/status/1552010650116816896

Quote
Lunar Reconnaissance Orbiter images of pits indicate that the Moon has caves. Could they become astronaut habitats?

Scientists have discovered that parts of the pits are always about 63°F (17°C), differing from extreme temperatures at the Moon's surface

https://www.nasa.gov/feature/goddard/2022/lro-lunar-pits-comfortable

Quote
Jul 26, 2022

NASA’s LRO Finds Lunar Pits Harbor Comfortable Temperatures

NASA-funded scientists have discovered shaded locations within pits on the Moon that always hover around a comfortable 63 F (about 17 C) using data from NASA’s Lunar Reconnaissance Orbiter (LRO) spacecraft and computer modeling.

The pits, and caves to which they may lead, would make thermally stable sites for lunar exploration compared to areas at the Moon’s surface, which heat up to 260 F (about 127 C) during the day and cool to minus 280 F (about minus 173 C) at night. Lunar exploration is part of NASA’s goal to explore and understand the unknown in space, to inspire and benefit humanity.

Pits were first discovered on the Moon in 2009, and since then, scientists have wondered if they led to caves that could be explored or used as shelters. The pits or caves would also offer some protection from cosmic rays, solar radiation and micrometeorites.

“About 16 of the more than 200 pits are probably collapsed lava tubes,” said Tyler Horvath, a doctoral student in planetary science at the University of California, Los Angeles, who led the new research, recently published in the journal Geophysical Research Letters.

“Lunar pits are a fascinating feature on the lunar surface,” said LRO Project Scientist Noah Petro of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Knowing that they create a stable thermal environment helps us paint a picture of these unique lunar features and the prospect of one day exploring them.”

Lava tubes, also found on Earth, form when molten lava flows beneath a field of cooled lava or a crust forms over a river of lava, leaving a long, hollow tunnel. If the ceiling of a solidified lava tube collapses, it opens a pit that can lead into the rest of the cave-like tube.

Two of the most prominent pits have visible overhangs that clearly lead to caves or voids, and there is strong evidence that another’s overhang may also lead to a large cave.

“Humans evolved living in caves, and to caves we might return when we live on the Moon,” said David Paige, a co-author of the paper who leads the Diviner Lunar Radiometer Experiment aboard LRO that made the temperature measurements used in the study.

Horvath processed data from Diviner – a thermal camera – to find out if the temperature within the pits diverged from those on the surface.

Focusing on a roughly cylindrical 328-foot (100-meter)–deep depression about the length and width of a football field in an area of the Moon known as the Mare Tranquillitatis, Horvath and his colleagues used computer modeling to analyze the thermal properties of the rock and lunar dust and to chart the pit’s temperatures over time.

The results revealed that temperatures within the permanently shadowed reaches of the pit fluctuate only slightly throughout the lunar day, remaining at around 63 F or 17 C. If a cave extends from the bottom of the pit, as images taken by LRO’s Lunar Reconnaissance Orbiter Camera suggest, it too would have this relatively comfortable temperature.

The team, which included UCLA professor of planetary science David Paige and Paul Hayne of the University of Colorado Boulder, believes the shadowing overhang is responsible for the steady temperature, limiting how hot things gets during the day and preventing heat from radiating away at night.

A day on the Moon lasts about 15 Earth days, during which the surface is constantly bombarded by sunlight and is frequently hot enough to boil water. Brutally cold nights also last about 15 Earth days.

The research was funded by NASA’s Lunar Reconnaissance Orbiter project, Extended Mission 4. LRO is managed by NASA's Goddard Space Flight Center in Greenbelt, Maryland, for the Science Mission Directorate at NASA Headquarters in Washington. Launched on June 18, 2009, LRO has collected a treasure trove of data with its seven powerful instruments, making an invaluable contribution to our knowledge about the Moon. Diviner was built and developed by the University of California, Los Angeles, and NASA's Jet Propulsion Laboratory in Pasadena, California.

NASA is returning to the Moon with commercial and international partners to expand human presence in space and bring back new knowledge and opportunities.

Bill Steigerwald

NASA Goddard Space Flight Center, Greenbelt, Maryland

[email protected]

Last Updated: Jul 26, 2022
Editor: Bill Steigerwald

First image caption:

Quote
NASA’s Lunar Reconnaissance Orbiter Camera has now imaged the Marius Hills pit three times, each time with very different lighting. The center panel, with the Sun high above, gives scientists a great view of the Marius Hills pit floor. The Marius pit is about 34 meters (about 111 feet) deep and 65 by 90 meters (approximately 213 by 295 feet) wide.
Credits: NASA/GSFC/Arizona State University

Second image caption:

Quote
This is a spectacular high-Sun view of the Mare Tranquillitatis pit crater revealing boulders on an otherwise smooth floor. This image from LRO's Narrow Angle Camera is 400 meters (1,312 feet) wide, north is up.
Credits: NASA/Goddard/Arizona State University

Offline Lampyridae

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Re: Lunar Caves
« Reply #7 on: 08/23/2022 03:17 pm »
Setting up a thread for discussing lunar caves, namely the lava tubes and skylights.  If any missions, such as the proposed Moon Diver, get underway for visiting them post here too.

The first 2 questions I wish to poise are:

1) How many skylights and lava tube locations are currently known on the Moon?

1) There's about 200. I have a tab open on another device where you can actually search for pits. It's a very handy tool.

Quote
2) Are any sites known to exist within the South Pole–Aitken basin?

2) Not that I'm aware of, but there are impact melt pits on the lunar Farside, especially in King Crater which has over a dozen IIRC.

Imagine the numbers of Bigelow inflatables that could be chained like sausages into such a cave. Plenty enough for a space colony, easier than in deep space or lunar surface, much closer than Mars... of course the interior of the cave would need serious "cleaning" in the first place.

Lava tubes tend to be smooth-floored, if a bit uneven (if made of the smooth ropey pāhoehoe kind versus the chunky ʻaʻā). A nearby collapse might have spread debris much like a rockburst in a mining tunnel, but generally intact sections will have glassy-smooth surfaces unless the lava river was carrying lighter rocks in its flow, or rapidly cut into a layer of ʻaʻā. Since tectonics and traditional erosional forces are non-existent on the Moon, a lava tube could be billions of years old unless it's smashed up by a meteorite impact.

Since they tend to be vitreous, lava tubes would be easy to make airtight. Polygonal cracks tend to form as the lava cools and contracts, which would need a bit of sealing or local remelting with a laser.

Another aspect of lava tubes is that, you can have repeated or parallel flows and thus get a honeycomb cross-section of lava tubes. The way they form, such digging through a rift, can leave them with a very organic HR Giger look.

Offline libra

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Re: Lunar Caves
« Reply #8 on: 08/23/2022 03:40 pm »
And... off we go, into the tech paper fest !
« Last Edit: 08/23/2022 03:41 pm by libra »

Offline libra

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Re: Lunar Caves
« Reply #9 on: 08/23/2022 03:46 pm »
Moar papers...

Offline Lampyridae

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Re: Lunar Caves
« Reply #10 on: 08/23/2022 03:50 pm »
I'm not sure if the lava tubes picked up by the GRAIL gravity surveys are among that lot, so here's the link:

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016GL071588#grl55400-tbl-0001

Anomaly                   Type          Long          Lat   Approx. Length (km)

Schröter Extension.....linear   306           24   60
Rima Mairan           linear    314           36   170
Rima Marius           linear    306           17   50
Marius Hills Skylight   linear    302           14   60
Rima Aristarchus   forked       313           27   100
Mairan-Rumker N-S   linear   309           41   90
Mairan-Rumker E-W   linear    306           41   180
Wollaston D           linear    311           35   80
Hershel E                   linear    324.5        33.5   20
Rima Delisle          linear    128           31   50
Cavalerius E          linear    279.5        8.5   75

These things are huuuuuuuge.
« Last Edit: 08/24/2022 07:16 am by Lampyridae »

Offline libra

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Re: Lunar Caves
« Reply #11 on: 08/23/2022 04:21 pm »
Yes. They are my signature. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016GL071588#grl55400-tbl-0001

The entire paper is here, for free. https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2016GL071588

The coordinates are quite intriguing: a large part of those tentative huge lava tubes are in a small corner of the Moon.

See the attached map. Most of them are (broadly) in the red rectangle.

Which mean that Oceanus Procellarum / Ocean of storms underground is kind of giant Swiss cheese.


Offline libra

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Re: Lunar Caves
« Reply #12 on: 08/23/2022 04:23 pm »
The lunar equator being 11 000 km long, divided by 360 is 30 km. So 1 degree of latitude / longitude = 30 km.

Now, all the holes are (broadly) in a square 20 * 20 degree north/south & east/west : 600 km on one side. A bit smaller than France (1000 km *1000 km) when the overall Moon surface is close from Africa (a 30 million km2 ballpark)
« Last Edit: 08/25/2022 10:28 am by libra »

Offline Lampyridae

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Re: Lunar Caves
« Reply #13 on: 08/29/2022 02:22 pm »
Here's another one. Looking for possible small cave systems associated with impact melt lavas, Bouguer gravity anomalies and

Possible cave systems under Copernicus, King and Severinus associated with pits.

The coordinates are quite intriguing: a large part of those tentative huge lava tubes are in a small corner of the Moon.

See the attached map. Most of them are (broadly) in the red rectangle.

Which mean that Oceanus Procellarum / Ocean of storms underground is kind of giant Swiss cheese.

The explanation for this is given in the attached appendix of the paper: they started off searching Oceanus Procellarum and are moving on to other areas. Gravity forward modelling is fiddly and time-consuming since they have to try and tease out the buried void, often running hundreds of models.
« Last Edit: 08/29/2022 02:26 pm by Lampyridae »

Offline Paul451

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Re: Lunar Caves
« Reply #14 on: 08/29/2022 11:40 pm »
There would be no advantage to having a pit in SPA, it's a scientifically interesting area but far from being the ideal place for a human habitat, if that was the goal.

You want a lava tube at a high enough latitude that the internal temperature stays below the freezing point of water. That should cause water vapour released from comet/wet-asteroid impacts to have collected over the last billion-or-so years. "Free" water, "free" cooling for the base, plus the ice (and trapped volatiles) might give you a very clean record of the impact history for the moon. Possibly much cleaner layering than the permanently-shadowed polar deposits, due to micrometeor impacts churning the surface and mixing layers.

The average low-latitude temp is around 15°C, which is reflected in pit-temps. Too high for water-ice to accumulate.

But I don't know how high latitude you have to go before the average surface temp (and hence constant sub-surface temp) gets below 0°C.

Libra/Lampyridae? Is the temp-vs-latitude info in your collections?
« Last Edit: 08/29/2022 11:43 pm by Paul451 »

Offline Lampyridae

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Re: Lunar Caves
« Reply #15 on: 08/30/2022 09:18 am »
There would be no advantage to having a pit in SPA, it's a scientifically interesting area but far from being the ideal place for a human habitat, if that was the goal.

You want a lava tube at a high enough latitude that the internal temperature stays below the freezing point of water. That should cause water vapour released from comet/wet-asteroid impacts to have collected over the last billion-or-so years. "Free" water, "free" cooling for the base, plus the ice (and trapped volatiles) might give you a very clean record of the impact history for the moon. Possibly much cleaner layering than the permanently-shadowed polar deposits, due to micrometeor impacts churning the surface and mixing layers.

The average low-latitude temp is around 15°C, which is reflected in pit-temps. Too high for water-ice to accumulate.

But I don't know how high latitude you have to go before the average surface temp (and hence constant sub-surface temp) gets below 0°C.

Libra/Lampyridae? Is the temp-vs-latitude info in your collections?

Only the top 30cm or so of regolith actually heats up during the day. Even in the Sea of Tranquility at noon, you could dig a small hole and hit soil that's subzero all day long. Lunar caves with a decent size opening actually work as kind of a greenhouse, with calculated equilibrium temperatures there at 293K/20°C. So if you come across a void with only a small opening then you might find trapped ice. Likewise at high latitudes, eg 45°, the light won't hit the floor so it won't have much input energy to heat up. Then equilibrium temps are like 240K at that latitude.

The highly insulating nature of regolith also means you wouldn't be able to thermally detect these buried lava tubes.

Equilibrium temperature of lunar caves

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022GL099710

Thermal gradient example

https://www.mdpi.com/2072-4292/12/4/731/htm#fig_body_display_remotesensing-12-00731-f010
« Last Edit: 08/30/2022 09:20 am by Lampyridae »

Offline Paul451

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Re: Lunar Caves
« Reply #16 on: 08/31/2022 06:11 am »
Thanks for that.

Am curious how far from a pit you'd need to go before a lava tube could reach ambient sub-surface temps, if at all. The Tranquility-paper modelled a few hundred metres from the pit, but there was virtually no fall-off, which is a concern.

I disagree with the Tranquility-paper about the suitability of ~20°C for long term habitation. Human activity produces waste heat, with the insulating effects of the surrounding rock, you want a cold sink. That's a bonus from any non-polar water-ice containing environment.

[In theory, a warmer (~20°C) tube might provide a good, thermally stable site for short-duration stay, small base infrastructure. But IMO you probably aren't going to be building such a base in a novel environment like a lava-tube. You need to have plenty of exploration of lava-tubes before you'd be comfortable designing a base (and pit access) suitable for them. That exploration requires a non-lava-tube base; so to explore lava-tubes, you've already solved the problem of short-stay surface bases anyway.]

Offline Lampyridae

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Re: Lunar Caves
« Reply #17 on: 09/01/2022 09:50 am »
Thanks for that.

Am curious how far from a pit you'd need to go before a lava tube could reach ambient sub-surface temps, if at all. The Tranquility-paper modelled a few hundred metres from the pit, but there was virtually no fall-off, which is a concern.

I disagree with the Tranquility-paper about the suitability of ~20°C for long term habitation. Human activity produces waste heat, with the insulating effects of the surrounding rock, you want a cold sink. That's a bonus from any non-polar water-ice containing environment.

[In theory, a warmer (~20°C) tube might provide a good, thermally stable site for short-duration stay, small base infrastructure. But IMO you probably aren't going to be building such a base in a novel environment like a lava-tube. You need to have plenty of exploration of lava-tubes before you'd be comfortable designing a base (and pit access) suitable for them. That exploration requires a non-lava-tube base; so to explore lava-tubes, you've already solved the problem of short-stay surface bases anyway.]

The pit receives ~1MW of sunlight energy during the day, so a small human presence wouldn't raise the temperature that much.

They could condition the ambient temperature by drawing a shade over the pit during the day and opening it at night.

Larger habitats would require radiators (plumbed to the surface), but that was never not going to be the case on the Moon.

Offline libra

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Re: Lunar Caves
« Reply #18 on: 09/03/2022 07:42 pm »
Haruyama (2012 paper) says there might be 4000 tons of water at the bottom of the Marius Hills Hole - the result of 1 billion year of solar wind eroding the regolith.


Offline TrevorMonty

Re: Lunar Caves
« Reply #19 on: 09/03/2022 10:04 pm »
Thanks for that.

Am curious how far from a pit you'd need to go before a lava tube could reach ambient sub-surface temps, if at all. The Tranquility-paper modelled a few hundred metres from the pit, but there was virtually no fall-off, which is a concern.

I disagree with the Tranquility-paper about the suitability of ~20°C for long term habitation. Human activity produces waste heat, with the insulating effects of the surrounding rock, you want a cold sink. That's a bonus from any non-polar water-ice containing environment.

[In theory, a warmer (~20°C) tube might provide a good, thermally stable site for short-duration stay, small base infrastructure. But IMO you probably aren't going to be building such a base in a novel environment like a lava-tube. You need to have plenty of exploration of lava-tubes before you'd be comfortable designing a base (and pit access) suitable for them. That exploration requires a non-lava-tube base; so to explore lava-tubes, you've already solved the problem of short-stay surface bases anyway.]
Surface access is biggest issue with lava tubes as most are only accessable via pits. Really need to bore a sloped tunnel to allow vehicle access to surface.

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